In the past, Sonia Chang-Diaz, Senate chair of the education committee, has insisted she wants to get a charter bill done. Her legislation renders that claim hard to believe. It’s a poison pill through and through, an offer the charter schools can’t help but refuse.

Here’s the most puzzling aspect of it all. Legislation usually improves after a tour through the Senate Ways and Means policy shop. Not this bill. So what happened?

Stephen Brewer, chairman of Senate Ways and Means, wouldn’t get into details, but emphasized that because his committee gives great latitude to committee chairmen, the bill that Ways and Means released is what Chang-Diaz wanted. But he sounded somewhat frustrated by the way it turned out.

“Policy is the great art of compromise,” Brewer noted. “It would be advisable to see other people’s positions and views, and try to compromise.”

Why is this legislation so toxic? For starters, it reinserts Chang-Diaz’s ill-considered reimbursement roadblock: In any year when the formula that pays district schools for students who have left for charters isn’t fully funded, charter expansion will stop.

Chang-Diaz’s legislation is a poison pill.

As they debate this, senators need to bear in mind that under our reimbursement formula, district schools receive 225 percent of a student’s annual educational costs after he leaves. Even if that formula, which spreads the payments over six years, isn’t always fully funded, it’s still extraordinarily generous. Charters, contrariwise, lose dollars for a departing student almost immediately.

At the very least, in tight years, Chang-Diaz’s provision would create havoc with charter-expansion plans. And in flush years, charter foes could conceivably stall expansion by contriving to underfund the formula slightly.

Then there are several not-so-hidden daggers aimed at all charters. For example, districts wouldn’t have to provide transportation for charter students during periods when the district schools aren’t in session. Further, depending on one’s interpretation, the districts might be exempt from transporting charter students if their schools have longer days.

That’s hugely counterproductive. Senators need to realize that taxpayers get a big bargain with charters, which provide longer days and years than the traditional schools and, as one would expect given that additional school time, frequently achieve better results. That expanded learning time is often cost-prohibitive for the traditional schools, but charters do it for the same per-pupil dollars. These new restrictions would make it more difficult for charters to offer that extra school time.

Next up: A charter school couldn’t be renewed if its three-year attrition rate was greater than that of the sending district. Here, several points are instructive. First, delve into the data, and charter attrition isn’t much different from district school attrition. Second, comparing an individual charter’s attrition rates to that of an entire district is classic apples to oranges. That measure wouldn’t count a student who left one district school for another as having attrited.

As senators debate the legislation, they need to recognize what an important prod to reform the charter movement has been. They should review the careful Harvard and MIT studies showing that Boston charter students outperform comparable students in the traditional schools.

They need to look beyond misleading rhetoric about “creaming” and “privatization” and understand that charters select their students by blind lotteries; that charters are public schools, accountable to the Board of Education; and that only three of the 71 Commonwealth charter schools are run by for-profit firms.

They should know that charters aren’t draining money that somehow belongs to the traditional schools but rather that a charter’s funding reflects the cost of educating the students who have chosen that school.

Lawmakers also need to come to grips with this lamentable reality: Trying to address every objection of the anti-charter camp is an endless Whac-a-Mole exercise, for this reason: Many charter foes simply have no interest in getting to yes.

In contrast to Chang-Diaz’s effort, the House legislation takes a realistic approach to legitimate concerns about fewer English language learners in charters, as well as to discouraging charter attrition. If the Senate does its research, it will remove the legislative poison pills and pass workable, House-like legislation.

If not, senators will deserve the same grade Senator Chang-Diaz has earned: an epic fail.